A hydraulic tensioner is a tension maintaining mechanism based on a basic principle of pressing a plunger to an endless belt by means of a spring and the hydraulic pressure. Various hydraulic tensioners of different structures have been proposed thus far (see, for example, Japanese Patent Application Publication No. 2000-170855).
The contents of Japanese Patent Application Publication No. 2000-170855 are incorporated herein by reference in their entirety.
In FIG. 1 of Japanese Patent Application Publication No. 2000-170855, a hydraulic tensioner includes a tensioner body, a plunger, hydraulic chambers and, a relief passage, and a relief valve. A cylinder hole is formed in the tensioner body. The plunger is slidably and reciprocably fitted into the cylinder hole. The plunger sticks out of the head-end surface of the tensioner body, and is capable of pressing an endless flexible member for transmission. The hydraulic chambers are formed between the cylinder hole and the plunger. The hydraulic pressure of the hydraulic oil in the hydraulic chambers acts in a direction such as to make the plunger stick out. The relief passage communicates with the hydraulic chambers. The relief valve includes a relief spring and a valve body. The valve body opens and closes the relief passage in accordance with the difference between the force to close the valve generated by the biasing force of the relief spring and the force to open the valve exerted by the hydraulic pressure of the hydraulic chambers. The relief valve is provided not in the plunger but in the tensioner body.
Meanwhile, as FIG. 1 of Japanese Patent Application Publication No. 2000-170855 clearly shows, the relief valve is provided in the tensioner body, but is located away from the plunger in a direction that is orthogonal to the longitudinal direction of the plunger.
This placement of the relief valve outside of the plunger makes the size of the tensioner body larger in the direction that is orthogonal to the longitudinal direction of the plunger. As a consequence, the hydraulic tensioner is made larger in size.
To reduce the size of the internal combustion engine, it is desirable to make the tensioner even smaller in size.